In general, a filter unit performs a filtering process of removing foreign substances from a fluid supplied to, for example, a ship by filtering the foreign substances present in the fluid.
For example, when the filter unit is installed in the ship, the filter unit may perform a filtering process of removing foreign substances from a fluid supplied to the ship, in order to allow ballast water to be stored in the ship after foreign substances have been removed therefrom. The ballast water functions to adjust the balance of the ship and the discharge of water from the ship as the amount of ballast water stored in a ballast tank, which is installed in the ship, is adjusted according to the amount of cargo loaded in the ship. The process of adjusting the amount of ballast water stored in the ballast tank may be performed by discharging the ballast water stored in the ballast tank to the outside of the ship or by supplying a fluid, such as seawater or fresh water, outside the ship to the ballast tank.
In this process, the filter unit installed in the ship removes foreign substances, such as inorganic matters including gravels, sand, mud, etc., organisms including fish and shellfish, crustacean, plankton, etc., and organic matters, from the fluid supplied to the ballast tank, thereby preventing the occurrence of damages, such as the disturbance of ecosystems and the distribution of harmful pathogens via the ballast water. In connection with this, the background technology of the present invention is disclosed in Korean Patent Registration Publication No. 10-0769834 (published on Oct. 24, 2007).
FIG. 1 is a conceptual view illustrating the implementation of a filtering process by a conventional filter unit, and FIG. 2 is a conceptual view illustrating the implementation of a backwash process by the conventional filter unit.
As illustrated in FIG. 1, the conventional filter unit 10 performs a filtering process on a fluid by moving the fluid so as to pass through passage holes 12 formed in a filter member 11. After being supplied into the filter member 11 through a penetration opening 13, the fluid moves from the inside of the filter member 11 to the outside of the filter member 11 through the passage holes 12 while moving from the bottom side to the top side of the filter member 11. The passage holes 12 have a smaller size than the size of the foreign substances to be removed from the fluid. Thereby, while the fluid moves from the inside of the filter member 11 to the outside of the filter member 11, the foreign substances mixed in the fluid cannot pass through the passage holes 12, thereby being removed from the fluid.
The foreign substances, which remain inside the filter member 11 due to the implementation of the filtering process described above, are adhered to the inner surface of the filter member 11, thus gradually clogging the passage holes 12. Due to this, the conventional filter unit 10 suffers from a gradual reduction in the flow rate of the fluid passing through the filter member 11, thus causing deterioration in function with regard to the filtering process.
To prevent the problem described above, the conventional filter unit 10 performs a backwash process on the filter member 11 as illustrated in FIG. 2. In this case, the fluid moves from the outside of the filter member 11 to the inside of the filter member 11, thus causing the foreign substances adhered to the inner surface of the filter member 11 to be separated from the filter member 11. That is, the fluid separates the foreign substances from the filter member 11 by moving in the direction opposite to the direction in which the fluid moves during the implementation of the filtering process. The foreign substances separated from the filter member 11 move along with the fluid as the fluid moves from the top side to the bottom side of the filter member 11, thereby being discharged outward through the penetration opening 13.
Here, when the conventional filter unit 10 performs the backwash process, the portion of the filter member 11 that is more distant from the penetration opening 13 exerts a smaller suction force, which is required to move the fluid from the outside of the filter member 11 to the inside of the filter member 11. As such, the fluid outside the filter member 11 moves into the filter member 11 at a lower flow rate at the portion of the filter member 11 that is more distant from the penetration opening 13. That is, the efficiency of backwashing is deteriorated with a decreasing distance to the top side of the filter member 11. Therefore, after the conventional filter unit 10 performs the backwash process, the foreign substances remain adhered to the upper portion of the filter member 11, and the passage holes 12 are clogged by the foreign substances, resulting in deterioration in filtering functionality.